From: Dave Hansen In order to turn an 8-way x440 into a 4-way for testing, we often use mem=(1/2 of total) and maxcpus=4. maxcpus has always worked, but mem= hasn't. The mem= parameter actually changes the kernel's e820 structure, which manifests itself as max_pfn. node_end_pfn[] obeys this because of find_max_pfn_node(), but node_start_pfn[] wasn't modified. If you have a mem= line that causes memory to stop before the beginning of a node, you get a condition where start > end (because start was never modified). There is a bug check for this, but it was placed just _before_ the error was made :) Also, the bootmem alloc functions die if you request something of zero size from them. This patch avoids that too. This shouldn't have much of an effect on non-NUMA systems. arch/i386/mm/discontig.c | 10 ++++++++-- mm/page_alloc.c | 7 +++++-- 2 files changed, 13 insertions(+), 4 deletions(-) diff -puN arch/i386/mm/discontig.c~discontig-empty-node-fix arch/i386/mm/discontig.c --- 25/arch/i386/mm/discontig.c~discontig-empty-node-fix 2003-06-10 23:33:16.000000000 -0700 +++ 25-akpm/arch/i386/mm/discontig.c 2003-06-10 23:33:16.000000000 -0700 @@ -114,10 +114,16 @@ void __init get_memcfg_numa_flat(void) */ static void __init find_max_pfn_node(int nid) { - if (node_start_pfn[nid] >= node_end_pfn[nid]) - BUG(); if (node_end_pfn[nid] > max_pfn) node_end_pfn[nid] = max_pfn; + /* + * if a user has given mem=XXXX, then we need to make sure + * that the node _starts_ before that, too, not just ends + */ + if (node_start_pfn[nid] > max_pfn) + node_start_pfn[nid] = max_pfn; + if (node_start_pfn[nid] > node_end_pfn[nid]) + BUG(); } /* diff -puN mm/page_alloc.c~discontig-empty-node-fix mm/page_alloc.c --- 25/mm/page_alloc.c~discontig-empty-node-fix 2003-06-10 23:33:16.000000000 -0700 +++ 25-akpm/mm/page_alloc.c 2003-06-10 23:33:16.000000000 -0700 @@ -1152,8 +1152,11 @@ static void __init calculate_zone_bitmap for (i = 0; i < MAX_NR_ZONES; i++) size += zones_size[i]; size = LONG_ALIGN((size + 7) >> 3); - pgdat->valid_addr_bitmap = (unsigned long *)alloc_bootmem_node(pgdat, size); - memset(pgdat->valid_addr_bitmap, 0, size); + if (size) { + pgdat->valid_addr_bitmap = + (unsigned long *)alloc_bootmem_node(pgdat, size); + memset(pgdat->valid_addr_bitmap, 0, size); + } } /* _